The present invention generally relates to a substrate transport apparatus and, in particular, relates to such an apparatus having means for compliantly urging the substrate against a registration member.
The transporting of a substrate such as, for example, an envelope, past a given point such as, for example, a read or write mechanism, is a problem encountered in many industries. This particular problem is frequently encountered, for example, in the mail handling industry. Typically, in this industry, the problem is encountered whenever it is desirable to read from, or print upon, an envelope when that envelope is moving past a read or write device.
The problem is complicated in instances where the thickness of the envelope varies due, for example, to such factors as the number, size or thickness of the contents of the envelope. This thickness variation alone can cause numerous difficulties and itself is further complicated by the fact that such stuffed envelopes tend to roll at the edges when pressure is uniformly exerted thereupon. The basic complication results from the need to restrict the region that is to be printed upon, or read from, to specific locations required by, for example, a regulatory agency, such as, the United States Postal Service (USPS). In many facilities, for example, the USPS employs optical readers to more efficiently sort large quantities of mail pieces according to information printed on the surface of envelopes or information on inserts that are visible through the windows of windowed envelopes. However, to maximize the reliability of using such readers, certain parameters of the information so printed must be regulated to ensure that the location thereof falls within the optical reading field of the reader. Usually, the location of such information is referenced to one or more edges of the envelope, for example, the upper right hand corner and/or the bottom edge.
The problem is still further complicated by the fact that the exact position of, for example, one or more inserts within identical envelopes is not necessarily uniform. As a result, the thickness profile of each envelope within an otherwise uniform group of mail pieces can, and does, vary within that group. Hence, the amount of curvature of a reference edge of such an envelope is not predictable.
Historically, at least in the mail handling industry, proof of payment indicia has been printed upon mail pieces by postage meters having either a drum, carrying an engraved pattern thereon, or by stamping each mail piece with a platen having an engraved pattern thereon.
However, even with large numbers of these meters still performing satisfactorily, the relatively recent advent of electronically controlled printing techniques has, in some instances, becoming prevalent. Along with this advance has been the development of contactless printing techniques. One common contactless printing technique is the continuous ink jet printing.
In this technique, ink is continuously provided to a print head and, via the print head, is accurately directed to the surface of the substrate. Individual characters are formed in this technique by ejecting ink sequentially through a nozzle, i.e. each character is drawn individually. In such a technique, the distance between the ink jet print head and the substrate is not overly critical since the relative position of dots is fairly consistent, although certain limits nevertheless exist. One drawback of such an ink jet printer is the requirement for small mechanical tolerances of the interconnecting components to effectively draw the large number of requisite characters to be printed. In addition, high voltages and complex fluid handling systems are required. Consequently, such printers are rather expensive.
Conventionally, in the mail handling industry, the transport apparatus used with continuous ink jet printing mechanisms includes a movable, but nonetheless rigid, base plate. The base plate is usually designed to allow envelopes of different thicknesses to pass thereacross while exerting pressure that is uniform across the envelope thereupon so that the envelope surface falls within the printing accuracy tolerance of the continuous ink jet print head.
A less expensive contactless printing technique is generally known as the drop-on-demand ink jet printing head. This arrangement is generally less expensive because drops are merely ejected from a multiplicity of nozzles rather than the directed stream from the nozzle used in a continuous ink jet arrangement. Characters are formed by the relative movement of the array of nozzles and by allowing drops from preselected ones of the openings. That is, in the drop-on-demand technique, characters are formed dot per dot or by numbers of dots at a time whereas in the continuous ink jet technique, the particular line constituting a particular character is formed by deflecting ink flowing from an opening. The deflecting means in conjunction with the requisite control of ink pressure incurs substantial expense in the continuous ink jet technique. The use of drop-on-demand techniques, however, has been somewhat limited because the print head therefor must be quite accurately positioned proximate the envelope surface to avoid the relative misplacing of dots and, hence, to ensure an adequate print quality. Thus, the use of such a printing technique exacerbates the problems inherent with envelope thickness variations. In fact, conventional envelope transport techniques effectively prohibit the use of the less expensive drop-on-demand techniques in mailing systems due to the complications resulting from the thickness variations of stuffed envelopes.
Consequently, there is a considerable need for a substrate transport apparatus that not only enhances the results of continuous ink jet printing techniques but also allows the reliable use of drop-on-demand ink jet techniques for printing on substrates that vary in thickness. Such a substrate transport apparatus clearly offers considerable savings to a large number of mail handling facilities.